A Unique Titania-Based SCR NOx Catalyst for Diesel Exhaust Emission Control

The selective catalytic reduction (SCR) of nitrogen oxide (NO_x) with ammonia (NH₃) or urea ((NH₂)₂CO) as a reductant is becoming a promising method for near future diesel exhaust emission control. To achieve a higher conversion rate from NO_x to nitrogen gas (N₂) with less NH3 slip in the tail pipe, careful control of NH₃ or urea dosage is necessary. For this purpose, a conventional SCR NO_x catalyst usually needs an additional oxidation catalyst for the destruction of excess NH₃. With an objective to destroy the excess NH₃ as well as NO_x within a single body of catalyst, a unique titania (TiO₂)-based SCR NO_x catalyst was developed, which can be fit into a space for an NO_x only catalyst. A key mechanism of the destruction of excess NH₃ without further formation of NO_x is sort of a self-consuming action where the excess NH₃ is partly converted to NO and this secondarily produced NO reacts with the remaining NH₃ and finally is reduced to N₂. Such a self-controlling feature can be applied to diesel engine vehicles or machines where load changes are frequently observed. In addition, a preliminary result on another TiO₂-based SCR NO_x catalyst, which does not contain vanadium (V) is also introduced.